Excited-State Double-Proton Transfer in the 7-Azaindole Dimer in the Gas Phase. Resolution of the Stepwise versus Concerted Mechanism Controversy and a New Paradigm
Excited-State Double-Proton Transfer in the 7-Azaindole Dimer in the Gas Phase. Resolution of the Stepwise versus Concerted Mechanism Controversy and a New Paradigm
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DOI：
10.1246/bcsj.79.373
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发表时间：
2006-03
影响因子：
4
通讯作者：
H. Sekiya;Kenji Sakota
中科院分区：
文献类型：
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作者：
H. Sekiya;Kenji Sakota
7-氮杂环己烷二聚体(7AI2)是双氢键分子的原型。7Al2被认为是DNA碱基对的模型，激发态双质子转移(ESDPT)的机制引起了人们的极大关注。到目前为止，已经提出了两种ESDPT机制，即分步机制和协调机制。人们从实验和理论两方面对ESDPT的机理进行了深入的研究。然而，十多年来，反应机理一直存在争议。我们根据电子光谱和皮秒时间分辨光谱在气相中获得的新数据，对这两种机制进行了解析。用UV-UV烧孔光谱研究了不同7Al2同位异构体的激子共振相互作用，很好地表征了ESDPT反应的初始态。7Al2的最低激发态被归类为激子理论的弱耦合情况。根据皮秒时间分辨实验结果和H/D动力学同位素效应对ESDPT的影响，通过测量振动态选择色散荧光光谱，我们得出结论：7Al2中的ESDPT反应以协同机制进行。7AI 2的ESDPT具有动态协作的性质，这可能是由于两个运动质子与电子的重组耦合而产生的。我们提供了一种新的ESDPT范式，其中激子共振相互作用和质子隧穿两种量子效应与ESDPT反应有关。
The 7-azaindole dimer (7AI 2 ) is a prototype of double hydrogen-bonded molecules. 7AI 2 has been considered as a model DNA base pair and has attracted much attention to the mechanism of the excited-state double-proton transfer (ESDPT). Two ESDPT mechanisms, stepwise and concerted mechanisms, have been proposed so far. Great efforts have been devoted to clarify the mechanism of ESDPT using experimental and theoretical methods. However, the reaction mechanism had been controversial for more than a decade. We provide the resolution of the two mechanisms on the basis of new data obtained from electronic spectroscopy and picosecond time-resolved spectroscopy in the gas phase. The initial state of the ESDPT reaction has been well characterized by investigating the exciton resonance interaction with UV-UV hole-burning spectroscopy for various 7AI 2 isotopomers. The lowest-excited state of 7AI 2 has been classified into the weak coupling case of the exciton theory. We have concluded that the ESDPT reaction in 7AI 2 occurs via the concerted mechanism on the basis of the results of picosecond time-resolved experiments and the H/D kinetic isotope effect on ESDPT studied by measuring the vibronic-state selective dispersed fluorescence spectra. ESDPT of 7AI 2 has a "dynamic cooperative" nature that may arise from the coupling of the two moving protons with the reorganization of electrons. We have provided a new paradigm of ESDPT, where two quantum effects, the exciton resonance interaction and the proton tunneling, are concerned with the ESDPT reaction.